152. Thirty-fifth Annual Meeting 
later the oxygen supply is rising to its winter condition. In 
this it will go through the winter and come out in the spring. 
The effect of this variation of the oxygen on the life of the 
lake must be briefly told. My own studies have been entirely on 
the microscopic life, mainly on the crustacea, though to some ex- 
tent on the rotifers. If you study the lake in the early spring, 
when the conditions of temperature are uniform, you will find 
these animals through the lake at all depths, and in very con- 
siderable numbers; and as the spring warming of the lake goes 
on there is everywhere a great increase in animal life. The algae 
seem to afford an abundance of food, so that the animal life of 
the lower types extends to all depths. As the summer conditions 
come on and as the oxygen begins to be cut off in the lower water, 
the an'mal life then becomes, as you would expect, more scanty, 
and as the July and August conditions succeed, the life in the 
open water of the lower part of the lake becomes almost extinct. 
Tt almost startles the student to see how sharp is the division be- 
tween the inhabited and uninhabited portions of the lake. Ii 
you lower a hose into the lake and pump the water from various 
depths into a fine net you will catch a great abundance of ani- 
mals in the water from the lower part of the circulating layer. 
This stratum indeed is often more densely populated then any 
other portion and may contain thousands of crustacea and roti- 
fers per gallon. But if the hose is lowered another meter, or even 
a half meter, an entire change appears. The water is perfectly 
clear and appears to the eve as fit for hfe as that above it, but 
you may pump many gallons of the water without securing more 
than a very few animals and these mainly sickly or injured forms 
which have evidently been caught as they were slowing sinking 
to the bottom. One animal indeed you are likely to find in num- 
bers quite large when its large size is taken into account. Those 
of you who have studied the animal life of lakes know the trans- 
parent larvae of the insect Corethra, which is one of the most 
beautiful and rapacious creatures found in our lakes. This is 
practically the only animal that you will find inhabiting the 
lower water. It comes up into the surface water at night, feeds, 
renews its stock of oxygen, which it stores in sacs, and goes 
down again for the day into this water devoid of oxygen. In 
such water it seems to be thoroughly at home and indeed we have 
